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Rolls MB15b ProMatch 2-way XLR/RCA line-level converter

Item # 172MB15B

Cleanly hook up consumer audio sources like a CD player or phone to your pro audio gear, or vice versa.

Cleanly hook up consumer audio sources like a CD player or phone to your pro audio gear, or vice versa.

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4 questions - 5 answers

Item # 172MB15B

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About the Rolls MB15b ProMatch

James Ralston

Connect your consumer and pro audio gear with this versatile 2-way converter

The Rolls MB15b lets you make clean connections between your consumer electronics and your studio recording or pro audio mixing gear. This 2-way box has two "channels." Channel 1 accepts professional line-level stereo XLR connections and outputs consumer line-level signals through its left and right RCA jacks. Channel 2 does the exact opposite, so you can convert in either direction. There's also an extra consumer line-level 3.5mm input and RCA aux output. Volume knobs for each channel let you dial in the signals for optimum performance.

Product highlights:

  • two-way converter
    • "Channel 1" converts stereo XLR (pro line-level) inputs to stereo RCA (consumer line-level) outputs
    • "Channel 2" converts stereo RCA (consumer line-level) inputs to stereo XLR (pro line-level) outputs
    • "Channel 2" features an additional stereo 3.5mm line-level input and stereo RCA line-level output
  • independent level control knobs for Channels 1 and 2
  • warranty: 1 year
  • MFR # MB15B

What's in the box:

  • Two-way stereo converter
  • 59" DC Power cord (output: 15VDC/500mA)
  • Instruction sheet

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More details on the Rolls MB15b ProMatch

Russ B.

Product Research


Overview: The Rolls MB15b ProMatch lets you convert professional line-level signals (+4dB) into consumer-level RCA signals (-10dB) and vice-versa.

Inputs & Outputs: The MB15b features 2 converters, Channel 1 & 2, built into one chassis, allowing conversion in both directions.

  • Channel 1: This includes 2 balanced female XLR inputs for connecting +4dB signals. The Output side includes a pair of RCA jacks for outputting -10dB signals to consumer audio devices. A Level adjustment knob lets you dial in the proper signal level.
  • Channel 2: This section of the converter features a pair of RCA input jacks and a 3.5mm stereo audio input jack for running consumer-level signals into the converter. Outputs consist of a pair of balanced male XLR jacks for running the converted +4dB signal to professional line-level devices. A pair of female RCA output jacks is also provided, outputting signals from either set of input jacks on Channel 2. This is handy for converting signals from the 3.5mm stereo input into consumer-level -10dB RCA signals. Channel 2 also includes a Level adjustment knob for fine tuning the signal level.


  • Maximum Output:
    • Balanced: +18dB
    • Unbalanced: +12dB
  • Maximum Input:
    • Balanced: +22dB
    • Unbalanced: +22dB
  • Input Impedance:
    • RCA: 100 kΩ
    • XLR: 10 kΩ
    • 3.5mm Stereo: 10 kΩ
  • Output Impedance:
    • RCA: 100 Ω
    • XLR: 100 Ω
  • Noise Floor: -88dB
  • Gain:
    • +4dB Input: -8dB
    • -10dB Input: +20dB
  • THD: 0.003%
  • Power Adapter: +15VDC/500mA
  • Dimensions: W = 5.17", H = 1.68", D = 3.95"
  • Weight: 1 lbs.

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Customer Q&A

4 questions already asked

Has anyone tried using both channels at the same time, for different signals?
steve  Mar 22, 2021
1 answer
I have not but I don't see why it wouldn't work. I use mine for stereo and it does the job well.
brian  Mar 22, 2021
I want to use the MB15b's "Channel 2" to convert phono preamp RCA output to XLR (for digital recorder) and also have RCA output to stereo preamplifier. Is the additional output (RCA) of "Channel 2" controlled by the same volume adjustment or is it passive? And what is the output impedance of the RCA output on Channel 2?
tom  Jun 19, 2020
2 answers
The output impedance of the RCA out is 100 ohms. The single page ???manual??? leads me to believe the level of the RCA out of channel 2 is controlled via the channel 2 level control, but it doesn???t say that explicitly, and I haven???t personally tested it. Hope this helps.
chay  Jun 20, 2020
The additional output (RCA) is controlled by the same volume adjustment. I do not know what the output impedance is.
james  Jun 20, 2020
I need to add a powered sub to my monitors for studio mixing. My sub only has RCA in/out. If I'm reading the spec right, I'd send TRS/XLR out, then RCA cables to the sub and back then TRS/XLR to my monitors. Correct?
christopher  Mar 02, 2020
1 answer
This can work as long as your powered subwoofer's RCA outputs are still full range or at least full range minus the bass that the subwoofer produces (not all RCA outputs on subs act this way though). Some monitors have XLR outputs and if your's does, then you could always use those outputs and not need to use channel 2 on this converter.
jason  Mar 16, 2020 (Staff)

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